Display screen or portion thereof with transitional graphical user interface



FIG. 1 is the first image in a sequence for a display panel displaying a transitional graphical user interface, according to a first embodiment of our new design;

FIG. 2 is the second image in the sequence, according to the first embodiment of our new design;

FIG. 3 is the first image in a sequence for a display panel displaying a transitional graphical user interface, according to a second embodiment of our new design;

FIG. 4 is the second image in the sequence, according to the second embodiment of our new design; and,

FIG. 5 is the third image in the sequence, according to the second embodiment of our new design.

The appearance of the transitional image sequentially transitions between the images shown in FIG. 1-2 and FIG. 3-5. The process or period in which one image transitions to another image forms no part of the claimed design. The outermost broken lines showing the display screen are included for the purpose of illustrating portions of the article and form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a transitional graphical user interface, as shown and described. 